Compact multiwire proportional counters for the detection of fission fragments.

Two large area multistep position sensitive (two dimensional) multiwire proportional counters have been developed for experiments involving study of fission dynamics using general purpose scattering chamber facility at IUAC. Both detectors have an active area of 20x10 cm(2) and provide position signals in horizontal (X) and vertical (Y) planes, timing signal for time of flight measurements and energy signal giving the differential energy loss in the active volume. The design features are optimized for the detection of low energy heavy ions at very low gas pressures. Special care was taken in setting up the readout electronics, constant fraction discriminators for position signals in particular, to get optimum position and timing resolutions along with high count rate handling capability of low energy heavy ions. A custom made charge sensitive preamplifier, having lower gain and shorter decay time, has been developed for extracting the differential energy loss signal. The position and time resolutions of the detectors were determined to be 1.1 mm full width at half maximum (FWHM) and 1.7 ns FWHM, respectively. The detector could handle heavy ion count rates exceeding 20 kHz without any breakdown. Time of flight signal in combination with differential energy loss signal gives a clean separation of fission fragments from projectile and target like particles. The timing and position signals of the detectors are used for fission coincidence measurements and subsequent extraction of their mass, angular, and total kinetic energy distributions. This article describes systematic study of these fission counters in terms of efficiency, time resolution, count rate handling capability, position resolution, and the readout electronics. The detector has been operated with both five electrode geometry and four electrode geometry, and a comparison has been made in their performances.

Prognostic factors in head and neck soft tissue sarcomas.

BACKGROUND: Soft tissue sarcomas of head and neck constitute a heterogeneous group of rare malignant tumors occurring at rare sites. The purpose of this retrospective study is to evaluate the pathologic features, treatment modalities, outcome, patterns of failure, survival, and other prognostic factors. METHODS: The medical records of 72 patients whose tumors were diagnosed as head and neck sarcomas, treated at Tata Memorial Center between 1981 to 1995 were reviewed. Potential prognostic factors including age, gender, tumor size, histology, grade, and adjuvant treatment were evaluated. RESULTS: The overall and disease free survival at 5 years was 60% and 45%, respectively. The median survival and follow-up was 76 and 38 months, respectively. Thirty-two patients (44.4%) developed recurrence of which 13 patients were salvaged. The univariate and multivariate analysis showed tumor size and grade as important prognostic factors for the survival. CONCLUSIONS: Tumor size greater than 5 cm and high grade tumors were important prognostic factors for survival. Every effort should be made for early diagnosis and wide surgical excision. For localized recurrent tumors without evidence of distant metastasis, surgery should be attempted whenever possible. High rates of locoregional failure in head and neck area indicate the need for improved treatment strategies.

Cytogenetic studies on a patient with prepubertal breast cancer: a case report.

Cytogenetic studies were carried in a 10 year old girl with prepubertal breast cancer for assessing inherited genetic susceptibility to chromosome breakage. The girl presented with a tumour in the left breast. Histologically it was diagnosed as secretory carcinoma (SC). Chromosome anomalies observed in phytohemagglutinin (PHA-P) stimulated lymphocytes were del(2)(q33), del(3)(p24), del(7)(q22) and dup(12)(p11p12). The regions involved have been reported in breast tumors. These loci, detected in peripheral blood lymphocytes (PBL), could be the sites susceptible to breakage, its subsequent effect being manifested in the target (breast) tissue.